This application is a 371 of PCT/EP96/02030 filed May. 13, 1996.
The invention relates to a process for freeze-drying coffee extract which saves energy and time in comparison with the processes known up to now. The invention furthermore relates to the thus obtainable freeze-dried coffee extract in pellet form.
Freeze-dried coffee extract for use as xe2x80x9cinstant coffeexe2x80x9d is usually produced as granules, whereby aqueous coffee extract with a dry substance content of approximately 40 wt/vol. % is foamed to a foam weight of approximately 450 to 750 g/l, the composition is cooled for approximately 30 minutes on freezing belts to a foam temperature of approximately xe2x88x9245xc2x0 C. and the frozen product is ground at xe2x88x9240 to xe2x88x9250xc2x0 C. The thus obtained granules are screened at low temperatures in order to eliminate the fines with grain sizes of less than 0.5 mm and particles with grain sizes above 3 mm. The quantity of fines, i.e. of particles with grain sizes below 0.5 mm, usually accounts for 30 to 35 wt. % of the frozen total product. After screening, approximately 95% of the granules have grain sizes in the range from 0.5 to 3 mm, but often up to 5% of fines with grain sizes of 0.5 mm or less are still present. The proportion of particles between 0.5 mm and 1 mm is approximately 10 to 20% of the screened product. These granules are usually poured into trays and freeze-dried at operating pressures between 0.3 and 0.4 mbar (Capacitron values, corresponding to Thermotron values of approximately 0.4 to 0.6 mbar). The freeze-dried end-product normally has a density of approximately 230 to 260 g/l.
However, the conventional processes for producing freeze-dried coffee extract have major disadvantages.
As explained above, 30 to 35% of the granules occur as fines which must be eliminated by screening, recycled and reprocessed.
The process is cost-intensive, since the energy expended on grinding at low temperatures between approximately xe2x88x9240 and xe2x88x9250xc2x0 C. and the costs of the screening and grinding stages contribute substantially to the total production costs.
In view of the still present fines and the different granule size, the product is dried at low pressures (approximately 0.3 to 0.4 mbar). However, the low drying pressures result in relatively long drying times and relatively low ice temperatures, with operating pressures of 0.3 to 0.4 mbar corresponding to product temperatures at the sublimation front of xe2x88x9227.0 to xe2x88x9225.5xc2x0 C. (these ice temperatures can be determined very precisely without thermoelements using barometric temperature measurement (BTM), see e.g. H. M. Willemer, PDA Symposium, Tokyo, Nov. 14-16, 1994, page 296). The production of freeze-dried coffee granules according to the state of the art is also extremely cost- and energy-intensive in this process stage.
It was therefore the object of the invention to find a process for producing freeze-dried coffee extract with the help of which the above-cited disadvantages can be avoided but which delivers a product which satisfies the highest quality requirements.